How to make better tablets using QbD
and the Gamlen Tablet Press

by Michael Gamlen (Gamlen Tableting)
and Joe Domingue (SciMark International)

The solution to reliably identifying and solving many tableting problems lies in the nature of a conventional tablet press. Single punch and rotary tablet presses work on a similar principle which is to compress material to a particular thickness. This is determined by the upper punch position on a single punch tablet machine, and the distance between the upper and lower rollers on a rotary tablet machine. Very small differences in thickness, (even a few tenths of a millimetre), can have a dramatic effect on tablet properties.

What is needed is the ability to compress a series of tablets to different FORCES under controlled conditions

This would allow the experimenter to determine the effect of compaction over a measured RANGE of forces or pressures, and permit proper characterisation of the material being compressed.

Three tablet parameters need to be measured to fully characterise a material. These are:

  1. Compaction pressure
  2. Tensile strength
  3. Solid fraction












Tensile strength (or fracture stress) of a tablet is determined by measuring the breaking load of the tablet under controlled testing conditions.

This is useful because tensile fracture stress has been shown to be a linear function of compaction pressure, up to a limiting value of pressure. Once a formulation has been characterised, compaction of single tablet at a known compaction pressure enables its’ compression properties to be determined. The solid fraction of a tablet increases with increasing compaction pressure but in a non-linear fashion. In many cases in the literature, data are reported on tablets with extremely high solid fractions of 0.95 or more. Compaction under these conditions is likely to cause problems with capping or delamination, and poor water penetration. The optimum range for solid fraction is 0.85 – 0.90.

A recently launched laboratory tablet press (the Gamlen Tablet Press (GTP-1) is being employed by pharmaceutical scientists as an ‘at-line simulator’ for both product development and trouble shooting.











Why use a Gamlen Tablet Press?

It can save you time, money and materials. People need help to study tablets under properly controlled conditions in a laboratory.

Michael Gamlen invented the Gamlen Tablet Press (GTP) to help you understand the relationship between the properties of your drug, formulation, and manufacturing process. When you do this you can develop better products more quickly, and improve productivity of your tablet manufacturing operations.

The GTP is the first machine designed to make tablets on a small scale at a user-specified compaction force. This force determines both the physical strength and the dissolution behaviour of the tablet. These are the key properties which ensure the tablet reaches the patient and delivers the drug.

The machine works by monitoring the force in real time using a PLC.  The punch force and punch position are displayed in real time on a computer which is also used to input the compaction conditions. Using the GTP we make tablets of extraordinary reproducibility and consistency, within 1-2% force, and with no wastage. Batch yields are >99%.

For the measurement of tablet breaking load, the press records both force and displacement during both compression and fracture, and also provides the ejection force profile associated with tablet ejection

In the scale-up of tablet production, the press can be used to determine the relationship between tablets developed at the bench-top scale using a few grams of material (often at the early development stage) and the final tablet manufactured on a rotary tablet press. The latter uses hundreds of kilograms of material, making process development difficult because of practical difficulties in experimentation; smaller and different shaped tablets can, however, be scaled to the final desired tablet design if TFS is used as the basis for comparison.

If you want better tablet products and processes you need the Gamlen Tablet Press.

Download full article: How to make better tablets using QbD and the Gamlen Tablet Press

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